The present invention relates to the field of sterile ventilating of food-quality liquid storage tanks to prevent contamination of tank contents and more particularly it relates to a continuous multi-step filtering, radiating and heating process and associated forced air apparatus for introducing warm sterilized air into the head space of a bulk liquid storage tank, including special outlet venting, in manner to prevent microorganism proliferation or other contamination of food products or ingredients stored in the tank.
A storage tank for liquid food ingredients or products is subject to contamination, e.g. by bacterial multiplication, unless preventive measures are taken. In ordinary circumstances vacuum sealing is impractical in such tanks; typically they cannot be made and kept air free and sealed air tight. Sealing would create serious temperature and pressure related problems and would interfere with filling and emptying, so such tanks are normally vented. Even with tanks that are kept filled to capacity for long periods of time, there is typically some head space containing an amount of air which is subject to contamination. Then whenever any of the content is drawn off, the volume removed is replaced by atmospheric air entering through the vent system. Unless this replacement air is sterilized, it carries risk of contamination. Ordinary dust filters in the intake or the venting port are ineffective in filtering out harmful microorganisms.
Many conventional filters and associated mechanisms such as ductwork, blowers and motors, unless specially and properly designed, can actually harbor and nurture microorganisms that can enter and contaminate the tank. Positive prevention requires continuous, or at least frequent, introduction of sterilized air into the head space of the tank so as to purge and replace the accumulated head space air; the rate of air flow must be sufficient to more than keep up with the maximum rate of depletion or draw-off, otherwise sub-atmospheric pressure within the tank would tend to draw in potentially contaminated outside air.
U.S. Pat. No. 5,358,009 to Cambell for a LIQUID STORAGE VESSEL VENTING SYSTEM discloses a system of check valves intended to selectively vent the tank by directing incoming air through a filter to remove airborne contaminants at an intake port and directing exhaust air through a separate outlet port.
U.S. Pat. No. 6,142,169 to Lees et al for a STERILE TANK VENTING SYSTEM FOR A FILLING MACHINE discloses a gas supply system including a sterile filter and a steam supply.
It is a primary object of the present invention to provide a method and associated facilities for fully sterilizing air and moving the sterilized air into the head space of a food-quality liquid storage tank for the prevention of contamination, particularly by microorganism invasion and proliferation.
It is a further object to provide a process of sequential steps including filtering, pressurizing and sterilizing in an optimal manner for introducing sterilized air into the head space of the tank.
It is a further object to provide a forced air sterilizer embodiment suitable for deployment in a food-quality liquid storage tank located in an outdoor environment.
It is a further object to configure a forced air filtering and sterilizing unit in a manner to facilitate cleaning, maintenance and replacement of components such as lamps and filters.
The foregoing objects have been met by the present invention of a liquid storage tank ventilation sterilizer that provides an overhead hood to minimize weather and environmental disturbances. Incoming air is first drawn in by an electric blower through an intake filter, then forced through a main filter. The airflow is then sterilized by ultraviolet radiation and then heated before entering the tank where it drives out moisture and stagnant air through a specially designed weather-protective outlet vent fitted with a removable cone shaped dual-screen filter unit. A remote indicator light panel indicates normal operation and provides warning of any malfunction.